1. Field of the Invention
The present invention relates to a portable computer which has a card connection port and which can process moving-picture data by the use of a card connected to the card connection port, and also to a card for use in combination with the portable computer.
2. Description of the Related Art
In recent years, technology of portable computers has advanced, developing computers called "multimedia personal computers." A multimedia personal computer can display not only text data and graphics data, but also image data such as moving pictures and still pictures. To display image data, use is made of YUV signals which have been hitherto utilized in TV sets and VTRs. More specifically, an option board is connected to the personal computer to display the image data, whereas the RGB display circuit incorporated in the personal computer operates to display text data or graphics data. Among such option boards available is CL-450 (reg. trademark) development board manufactured by C-Cube Microsystems, U.S.A. This board uses MPEG (Moving Picture Coding Experts Group) video algorithm, expanding MPEG compress video signals and converting YUV signals into RGB signals, and outputs the RGB signals thus generated.
MPEG is the abbreviation for an organization subordinate to JTC1 (Joint Technical Committee) which is sponsored by ISO (International Organization for Standardization) and IEC (International Electro-technical Commission). MPEG sometimes means the coding scheme employed to accumulate color image data Two MPEG coding schemes are available The first scheme known as MPEG-1 is designed for application to CD-ROMs, with data transfer speed of 1.5 MB/sec. or less. The second scheme known as MPEG-2 is designed for processing high-quality image data, with data transfer speed ranging from 5 MB/sec. to 10 MB/sec.
Another of the option boards available is DVI (Digital Video Interactive) board manufactured by Intel, Inc., U.S.A. The DVI board has a 82750PB chip for compressing and expanding image data, a VRAM for storing image data, and a 8275DB chip for controlling the image-data display.
If such an option board is connected to the personal computer, the computer will have two display sub-systems, i.e., the RGB sub-system incorporated in the computer and the YUV sub-system mounted on the option board. The resultant circuit configuration is obviously redundant.
Advanced laptop portable computers have a flat-panel display such as a TFT color LCD. It is desired that the flat-panel display displays not only text data and graphic data but also image data such as moving pictures and still pictures, in any combination thereof.
Recently, personal computers having a slot for a PC card which conforms with the standards of JEIDA and the standards of PCMCIA (Personal Computer Memory Card International Association) are used in increasing numbers. Various devices have been developed to use this PC card in combination with a moving-picture capture card, an MPEG decoder and the like, which controls input and output of moving-picture data.
To use a PC card, a personal computer of the conventional standard bus specification (e.g., an ISA bus computer), the speed with which image data can be transferred through the bus is too low to display images having a resolution comparable with that of images the TV sets of NTSC system can display. The image data must therefore be processed at low speed, inevitably displaying images of low quality (i.e., low resolution). In order to display image of higher quality, it is necessary to replace the ISA bus with a high-speed bus such as CPI (Peripheral Component Interconnect) bus.
As described above, the personal computer of the conventional standard bus specification cannot display images having quality as high as ordinary TV images, when it uses a standardized PC card in order to process moving-picture data. To display images having quality as high as TV images, the computer must have its system bus replaced by a high-speed system bus. If provided with a high-speed system bus, the computer will be expensive, consume more power and become complex in structure.